The present invention relates to a method for improving the optical performance of an existing progressive lens or progressive lens design. The performance is expressed as a quantitative merit figure and is improved by selectively varying the shape of the lens surface to optimize the resulting lens' merit figure.
The method of the present invention may be applied to an ophthalmic progressive lens having distance, intermediate and near viewing regions. Methods of making progressive lens surfaces are described in Applicants' U.S. patent application Ser. No. 6/516,366 filed July 22, 1983 now U.S. Pat. No. 4,676,610, issued on June 30, 1987. This prior application is hereby incorporated by reference in the present application as if fully set forth. Lenses made according to methods described in application Ser. No. 6/516,366 have been used publicly and sold in the United States more than one year prior to the date of the present application.
"Improving" or "optimizing" a lens design involves some criterion of merit. Depending on the purpose intended for the lens, the merit criterion may weight various quantifiable lens characteristics more heavily than others. However, once such relative weightings have been chosen, a weighted combination of quantitative measures of lens performance can be formulated. An evaluation rule can thus be constructed that yields a single number which reflects the overall "quality" of the design according to the chosen weightings. Such a rule is often called a "merit function" and its value is often called a "merit figure". The merit function can be constructed such that either smaller or larger values of the merit figure indicate better lens performance. In this context, an "optimum" lens is one that minimizes or, if appropriate, maximizes the value of the merit function. A variety of such methods for minimizing or maximizing the values of such merit functions in general lens design are known in the prior art. The CODE V program available from Optical Research Associates, 550 North Rosemead Boulevard, Pasadena, Calif., is one such general lens design tool. The mathematics of such optimization procedures are discussed in, for example, Hamming, R. W., Numerical Methods for Scientists and Engineers, 2d ed., Dover Publications, New York 1973, Chapter 43.
Important quantitative measures of lens performance are astigmatism, orthoscopy, and mean curvature. These are optical measures which may be computed in two somewhat different ways. The first way, which may be termed surface measure, uses the properties of an optical surface unmodified by any effects of ray obliquity that may occur in actual use of the surface. It is known to compute such surface measures in the art of progressive lens design from the geometrical properties of the surface without reference to the overall physical configuration of use of the lens. The second way of computing the purely optical quantitative measures of lens performance may be called true optical measure which takes such ray obliquity effects into account. To compute true optical measures for an ophthalmic lens, the actual physical relationship of the lens to the eye in use must be simulated, so that correct ray angles are obtained. Ray tracing techniques may then be used to compute the true optical measures of performance.
In practice, a "family" of lens designs is constructed through a mathematical design model which contains a number of adjustable parameters that determine the quantitative performance measures of a particular design. Examples of such design models are given in Applicants' above referenced U.S. patent application.